Rotating shafts have torsional vibrations inherent due to their non-uniform construction (e.g. crankshafts, and camshafts), or the nature of the driving mechanism employed (e.g. firing order of an internal combustion engine, or gearing), or the method employed for their connection to another shaft (e.g. through a universal, or a constant-velocity joint). These torsional vibrations if left unattended reach a peak amplitude when their exciting frequency approaches the natural torsional frequency of the shaft. This phenomenon known as resonance can cause premature fatigue failure of the shaft, or can be felt as undesirable noise or vibration by a vehicle or machine operator.
Torsional Vibration Dampers (TVDs) are commonly employed to attenuate such undesirable vibrations. The objective of a TVD is break the vibratory amplitude peak at resonance to two (or more) smaller peaks each of which have sufficiently reduced amplitudes that can be sustained by the shaft.
In vehicle driveline applications, there are two common types of TVDs that are employed—internal and external. Internal TVDs are mounted on the surface defined by the Inner Diameter (“ID”) of the drive-shaft, prop-shaft, or half-shaft (“shaft”); while the external TVDs are mounted on the surface defined by the Outer Diameter (“OD”) of the shaft or on the OD of the flanges located on either end of the shaft. The disclosed invention only pertains to external TVDs.
The simplest version of an external TVDs comprises of two components, a metallic ring that provides the requisite amount of inertia necessitated for the TVD to be effective in the application, and an elastomer element (usually a ring or a strip) that is press-fitted between the shaft and the ring. The elastomer element serves two purposes: (1) it provides the spring-dashpot system for TVD to function; and (2) it provides the adequate hydro-static pressure by being assembled under compression that holds the TVD axially in place on the shaft.
The common materials used for the ring include but are not limited to steel, cast-irons, and aluminum alloys. The common materials used for the elastomer element include but are not limited to Ethelene Propylene Diene Monomer (“EPDM”), Styrene Butadiene Rubber (“SBR”), and Poly Butadiene (“PBD”).
FIG. 1 illustrates two examples of prior art. In the first example on the bottom right the TVD comprising of ring 1 and elastomer 2 is installed directly onto Shaft 3. This is because the OD surface 32 of shaft 3 is large enough to receive the ID surface 21 of elastomer 2.
In the second example on the top left is where the TVD is installed onto flange 5 instead of shaft 3. In this illustration, the OD surface 51 of flange 5 is not sufficiently large to receive the ID surface 21′ of elastomer 2′, an additional component namely the hub 4 is incorporated into the design. Hub 4 bears an OD surface 42 that is sufficiently large to receive the ID surface 21′ of elastomer 2′. Furthermore, the ID surface 41 of the hub 4 rigidly mounts (usually via a press-fit) on the OD surface 51 of flange 5.
Of these two constructions, the former is preferred over the latter (i.e. in FIG. 1 bottom right construction is preferred over the top left) for two reasons: (1) its cost-effectiveness, as it comprises of only two components, and (2) its ease of installation onto the shaft or flange (“S/F”), as an elastomer-to-metal press-fit is more forgiving than a metal-to-metal press-fit. The disclosed invention only pertains to TVDs that are installed without a hub directly onto S/F.
Installation of a traditional TVD is usually accomplished before the shaft accepts flanges on either end that have a diameter larger than the mounting diameter of the TVD, or the shaft is flared (deformed partially along its axial length to a diameter larger than the mounting diameter of the TVD). This greatly restricts the manufacturing process of the shaft, which now must be shipped to the TVD manufacturer for the TVD installation and then shipped back to the shaft manufacturer for the completion of its assembly; or alternately the TVD must be received as a component ready for installation onto the S/F early in the manufacturing process. This method of installation of the TVD onto the S/F is known as axial-installation, and is the traditional method employed in the industry.
The need for a TVD that can be installed onto the fully assembled S/F has been long realized. This need is particularly magnified during Noise Vibration and Harshness (NVH) related testing of the drive-shaft where TVDs of varying frequencies are mounted on the S/F to determine their NVH effectiveness. This need has traditionally been fulfilled by using a two-piece bolt-on design.
FIG. 2 illustrates a two-piece bolt-on design. Elastomer 2a usually comprises of two strips and is received directly on its ID surface by S/F 3a and ring 1a comprising of two mirrored half-rings that are held in place together by two bolts 6a. This allows elastomer 2a to be compressed by the bolt-preload, and hold the TVD axially in place on S/F 3a. This method of installation of the TVD onto the S/F is known as radial-installation
Such a design illustrated in FIG. 2 has three inherent problems: (1) it forces the manufacturing of the TVD to be overly expensive (considering the counterbored holes and the corresponding threaded holes); (2) it puts a limitation on size of the TVD (mass and geometric) as the half-rings must accept bolts of a reasonable size (required for the necessary preload); (3) it is overly cumbersome to install such a TVD in a manufacturing environment, as several components need to be precisely aligned before the fasteners may be loaded, coupled by the necessity of preloading both fasteners simultaneously for proper (uniform) compression of the elastomer. Consequently, the use of the two-piece bolt-on TVD has been limited to prototype testing where its ability to be radially mounted overweighs its associated shortcomings.
Furthermore, in many such S/F applications, it is often desired that the same components (same geometry and same material) of the TVD (ring and elastomer) be used with minor frequency adjustments across different vehicular platforms. Traditionally this could only be fulfilled via producing the same ring and coupling it with elastomers having the same geometry but varying hardness' (durometers) across different vehicular platforms. Thereby, adjusting the frequency of the TVD by altering material properties of the elastomer. This causes two additional problems: (1) it necessitates the generation of several part-numbers thereby complicating logistics; and (2) it is prone to human/machine error that TVDs from one platform may mistakenly be switched with those from another platform due to their identical visual appearance.